The present invention relates generally to fluids, on more specifically the invention pertains to a system and method to measure both the isothermal secant and tangent bulk modules and the density of functional fluids. The instrumentation and methodology described in this invention use much smaller volumes of fluids which permits the measurement of these critical properties on experimental fluids which are available in only limited quantities.
Bulk modulus is a property which describes the resistance of a liquid to compression. It is a reciprocal of compressibility. It may be determined by either isothermal (static) or adiabatic (dynamic or isentropic) methods. In either case, bulk modulus may be expressed as either secant or tangent functions.
The hydraulic systems required by modern aircraft and missile systems operate at temperatures and pressures which have become increasingly more elevated in response to the demands for increased performance. As a result, the need for the determination of physical properties at high pressures and temperatures has become a requirement of critical proportions. Specific needs include measurement of density, tangent bulk modulus, secant bulk modulus and viscosity.
The best example of prior art systems is in U.S. Pat. No. 5,383,352, dated Jan. 24, 1995, entitled Method for the measurement of bulk modules and pressure viscosity of liquids, Krawetz, Arthur A., the disclosure of which is incorporated herein by reference. This reference describes a method for determining bulk modulus of a liquid based on a pressure-volume-temperature relationship at constant volume corrected for changes in system volume due to elevate pressure and temperature. The apparatus used to determine bulk modulus comprises a pressure vessel in which the liquid to be tested is introduced, and from which all gases are removed. The vessel is placed in a constant temperature oven and the pressure is records.
The above-cited reference is a patent method for the measurement of bulk modulus and pressure viscosity of liquid. The method is based on a pressure-volume-temperature relationship at a constant volume. The apparatus comprises a constant temperature oven, a container vessel within the oven, a plurality of valves, a pump, a regulator and a viscometer. The apparatus is used to obtain a relationship expressing vessel volume at any specified temperature and pressure. This relationship is then used to determine bulk modulus and pressure viscosity.
Other prior art systems include the following U.S. patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,113,384 issued to Lauer et al. PA0 U.S. Pat. No. 4,113,384 issued to Lauer et al. PA0 U.S. Pat. No. 4,193,291 issued to Lynnworth PA0 U.S. Pat. No. 4,384,472 issued to Tournier PA0 U.S. Pat. No. 4,559,810 issued to Hinrichs et al. PA0 U.S. Pat. No. 5,383,452 issued to Krawetz.